<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div dir="ltr"></div><div dir="ltr">Have you checked for hi freq oscillations?</div><div dir="ltr"><br></div><div dir="ltr">Ian</div><div dir="ltr"><br></div><div dir="ltr"><br>On Jan 16, 2020, at 9:48 AM, Jean-Pierre Desrochers <<a href="mailto:jpdesroc@oricom.ca">jpdesroc@oricom.ca</a>> wrote:<br><br></div><blockquote type="cite"><div dir="ltr"><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><meta name="Generator" content="Microsoft Word 14 (filtered medium)"><style><!--
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</o:shapelayout></xml><![endif]--><div class="WordSection1"><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Hi list,<o:p></o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I'm working on the Elby-Design ASM-1 VCO<o:p></o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><a href="https://www.elby-designs.com/webtek/asm-1/vco/vco-asm1-cct.pdf">https://www.elby-designs.com/webtek/asm-1/vco/vco-asm1-cct.pdf</a><o:p></o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Im want to use it as a 1v/oct LFO (.05hz to 20hz)<o:p></o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I first mounted the circuit on my protoboard with success.<o:p></o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">at first I used a matched pair of 2N3904 for Q1A & Q1B<o:p></o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">instead of the MAT02 shown in the schematic.<o:p></o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I could reach very low frequencies (as low as .04hz).<o:p></o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">But to do so I needed to replace R9(56k) for a 33k temporarily. Fine. <o:p></o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">This morning I replaced both 2N3904 with a genuine MAT-02<o:p></o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">and started the same frequency measurements as yesterday.<o:p></o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I bumped into something weird..<o:p></o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Here are the actual measurements I first did using 2x2N3904:<o:p></o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">mVolt at 1k TEMPCO resistor vs Sawtooth period<o:p></o:p></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">158.0mV => 0.050sec<o:p></o:p></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">176.0mV => 0.100sec<o:p></o:p></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">193.8mV => 0.200sec<o:p></o:p></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">212.0mV => 0.400sec<o:p></o:p></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">229.8mV => 0.800sec<o:p></o:p></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">247.5mV => 1.6sec<o:p></o:p></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">265.5mV => 3.2sec<o:p></o:p></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">283.2mV => 6.4sec<o:p></o:p></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">301.7mV => 12.8sec<o:p></o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">319.7mV => 25.6sec<o:p></o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">(18mV steps, nice exponential response!)<o:p></o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Now here are the actual measurements with a MAT-02:<o:p></o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">mVolt at 1k TEMPCO resistor vs Sawtooth period<o:p></o:p></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">157.0mV => 0.050sec<o:p></o:p></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">175.0mV => 0.100sec<o:p></o:p></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">193.0mV => 0.200sec<o:p></o:p></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">211.0mV => 0.400sec<o:p></o:p></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">229.0mV => 0.800sec<o:p></o:p></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">247.0mV => 1.6sec<o:p></o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">271.0mV => 3.2sec<o:p></o:p></span></p><p class="MsoNormal"><b><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">*** Now trying to go further increasing the TEMPCO mVolts<o:p></o:p></span></b></p><p class="MsoNormal"><b><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">*** the oscillator starts backing up and re-increase its frequencies !!!<o:p></o:p></span></b></p><p class="MsoNormal"><b><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">*** I could not go further lowering the frequency. <o:p></o:p></span></b></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I tried 3 different MAT-02's and even LM394's<o:p></o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">and they all behave the same.<o:p></o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Using different matched pairs of 2N3904 worked perfectly..<o:p></o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I suspect MAT-02’s minimum base to emitter current reached (???)<o:p></o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">What am-I missing here ??<o:p></o:p></span></p><p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">By the way, all the IC's I'm using here are genuine one's<o:p></o:p></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">(TL082, MAT-02, CA3140, LM311).<o:p></o:p></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">JP<o:p></o:p></span></p></div></div></blockquote><blockquote type="cite"><div 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